INVESTIGADORES
MININNI Pablo Daniel
congresos y reuniones científicas
Título:
Structure functions and cancellation exponent in MHD: DNS and Lagrangian averaged modeling
Autor/es:
P.D. MININNI
Lugar:
Madison, Wisconsin
Reunión:
Workshop; CMSO workshop "Magnetic turbulence meeting"; 2005
Institución organizadora:
University of Wisconsin
Resumen:
The range of scales encountered in MHD problems of astrophysical
interest is well beyond expected computer resolutions in the next
decades. For this reason, closure schemes are often employed to
model the effect of the unresolved scales. One such closure is Lagrangian-averaged magnetohydrodynamics (LAMHD) or the "alpha
model.'' This model is an extension of the smoothing procedure in
fluid dynamics which filters velocity fields locally while
leaving their associated vorticities unsmoothed, and has proven
useful for high Reynolds number turbulence computations. It
differs from large eddy simulations in that it preserves the
invariants of a given flow. We present DNS and LAMHD simulations
of forced and free decaying two-dimensional magnetohydrodynamic
turbulence. The exponents of structure functions of the velocity,
the magnetic field, and the Elsasser variables are studied.
LAMHD is found to have the same intermittent behavior as the DNS. The statistics of sign cancellations of the current (and
vorticity) at small scales are also studied using both the
cancellation exponent and the fractal dimension of the
structures. LAMHD is found to have the same scaling behavior
between positive and negative contributions as the DNS. At large
Reynolds numbers, an independence of the cancellation exponent
with the Reynolds numbers is observed.